This invention relates to actuators for controlling the operation of valves and especially for valves used in sprinkler systems for fire protection.
Automatic sprinkler systems for fire protection of structures such as office buildings, warehouses, hotels, schools and the like are required when there is a significant amount of combustible matter present. The combustible matter may be found in the materials from which the building itself is constructed, as well as in the building contents, such as furnishings or stored goods.
Of the various types of automatic sprinkler systems available, the preaction systems find widespread use. Preaction systems use an actuator which responds to a combination of signals from different detectors to trip a valve which provides water to the sprinkler piping network. Similar to the so-called xe2x80x9cdry-pipexe2x80x9d systems, the piping network in the preaction system is normally filled with air or nitrogen (and not water) prior to actuation. The preaction system can thus be used in unheated environments which are subject to below freezing temperatures without fear of pipes bursting due to water within the pipes expanding upon freezing.
When sufficiently pressurized, the behavior of the gas within the piping network may be used to indicate a fire condition and trigger actuation of the preaction system. Heat from the fire will cause sprinkler heads to open, allowing pressurized gas to escape from the piping network and result in a pressure drop within the system. Actuation of the system may be effectively triggered by this pressure drop.
Specifically, double interlock preaction systems are further advantageous because an alarm may be sounded to provide a warning before the sprinklers operate. Furthermore, failure, breakage or accidental opening of the sprinklers or a pipe in the piping network will not result in an unintentional discharge of water, since there is no water in the network until the system is actuated. Actuation for double interlock preaction systems requires that two or more separate signals be sensed by the actuator.
Preaction systems are not without their disadvantages however. Traditional preaction systems, described above, which are triggered by a drop in air pressure within the piping network as the result of a sprinkler head opening in response to heat (along with a confirming signal from another sensor) usually maintain the sprinkler piping network at a relatively high internal pressure, typically on the order of 20% of the maximum water pressure in the system. The air pressure in such systems is used to control the release of the water to the piping network, and the valves typically operate at a mechanical advantage of about 1 to 5 air pressure to water pressure. The use of relatively high-air pressures becomes a problem with larger systems which tend to have a relatively large volume of air within the piping network. Higher air pressures and volumes require more powerful compressors, having higher capital and operating costs. Furthermore, the higher pressures mean that more air must be forced out of the piping network upon activation. The air in the network inhibits the free flow of water and, thus, increases the reaction time of the system. More air in the piping network also means that more moisture will be present, accelerating corrosion of the pipes.
There is clearly a need for a preaction sprinkler system having the ability to operate at relatively low system air pressures for providing a signal which activates the sprinkler system.
The invention concerns an electro-pneumatic actuator for actuating a fire sprinkler system. The system is actuated when the actuator depressurizes a piston holding a valve controlling the flow of water to the sprinkler system closed. The actuator behaves like an AND gate in a logic circuit in that it will depressurize the piston and release the valve only when two separate signals indicating a fire condition are manifest in the actuator. The actuator is, thus, connected to two separate fire detection systems, one being the piping network of the sprinkler system charged with compressed gas, the other being an electronic fire detection system having a control system in communication with a plurality of fire detectors substantially co-located with the piping network.
During a fire, heat-sensitive sprinkler heads on the piping network open and release pressurized air within the network to the ambient causing a pressure drop in the piping network. Because the piping network is in fluid communication with the actuator, the pressure drop is sensed by it. The pressure drop is accompanied by a signal or signals indicating a fire condition sent from one or more of the fire detectors to the control system. In turn, the control system sends an electrical signal to the actuator. In response to the concurrent pressure drop in the piping network and the electrical signal from the control system, the actuator depressurizes the piston which allows the valve to open and supply water to the piping network for release through the open sprinkler heads onto the fire.
In the preferred embodiment, the actuator has a first chamber with a flexible first diaphragm mounted therein. The first diaphragm sealingly divides the first chamber into first and second chamber portions, both the chamber portions being in fluid communication with the cylinder. The second chamber portion has an opening providing fluid communication with the ambient, the opening being surrounded by a seat facing the first diaphragm. The first diaphragm is deflectable into sealing engagement with the seat to seal the opening when the cylinder is pressurized with a first fluid, such as the water for the sprinkler system.
A second chamber having a flexible second diaphragm mounted therein which sealingly divides the second chamber into third and fourth chamber portions is preferably positioned above the first chamber. The third chamber portion is in fluid communication with a source of pressurized second fluid, for example, the compressed air within the piping network, and the fourth chamber portion is in fluid communication with the ambient. The fourth chamber portion has an aperture providing fluid communication with the first chamber portion, the aperture being surrounded by a second seat facing the second diaphragm. The second diaphragm is deflectable into sealing engagement with the second seat to seal the aperture when the third chamber portion is pressurized with the second fluid, for example, the compressed air from the piping network.
A third chamber having a flexible third diaphragm mounted therein which sealingly divides the third chamber into fifth and sixth chamber portions is preferably mounted atop the second chamber. The fifth chamber portion is in fluid communication with the pressurized first fluid. An elongated plunger extends between the fifth and third chamber portions. One end of the plunger is positioned within the sixth chamber portion and is engageable with the third diaphragm, the other end of the plunger being positioned within the third chamber portion and engageable with the second diaphragm. The third diaphragm is deflectable into engagement with the one end of the plunger when the fifth chamber portion is pressurized with the pressurized first fluid. The plunger is forced into engagement with the second diaphragm and thereby forces the second diaphragm into sealing engagement with the second seat.
A passageway is located within the third chamber providing fluid communication between the fifth chamber portion and the ambient. A valve is engaged with the passageway and has a valve member movable between an open position, allowing fluid flow through the passageway and a closed position, preventing fluid flow through the passageway. The valve also has means for biasing the valve member into the closed position and an electrically operated actuator for moving the valve member into the open position upon receipt of the electrical signal form the control system.
In operation, the second diaphragm is deflected out of engagement with the second seat only when fluid pressures in both the fifth and the third chamber portions are lowered to respective predetermined values, pressure in the fifth chamber portion being lowered by electrically actuating the valve member into the open position, pressure in the third chamber portion being lowered by a drop in pressure of the pressurized second fluid. Upon deflection of the second diaphragm, pressurized first fluid in the first chamber portion is permitted to enter the fourth chamber portion and exit to the ambient, thereby allowing the first diaphragm to deflect out of engagement with the first seat. This allows the pressurized first fluid to flow from the cylinder through the second chamber portion and exit to the ambient, thereby depressurizing the piston and allowing it to move within the cylinder to release the valve and actuate the sprinkler system.
The invention also includes a reset valve for manually resetting the sprinkler system and preventing unintentional resetting during a fire. The reset valve has a valve body and a conduit extending through the valve body. One end of the conduit is in fluid communication with the third chamber portions and the other end is vented to the ambient. A valve seat is positioned in the one end of the conduit and a valve closing member is movably mounted within the conduit adjacent to the seat. The valve closing member is movable into sealing engagement with the seat to close the reset valve. The reset valve also has means for biasing the valve closing member out of engagement with the seat when fluid pressure within the one end of the conduit falls below a predetermined value. The biasing means thereby opens the reset valve and vents the third chamber portion to the ambient. Preferably, there is an identical reset valve in fluid communication with the fifth chamber portion as well. The reset valves prevent spurious pressure surges from pressurizing either of the third or fifth chamber portions and thereby accidentally resetting the system and, thus, cutting off the water supply during a fire.
It is an object of the invention to provide an actuator for a double interlock fire protection sprinkler system which uses pneumatic and electrical functions to actuate the system.
It is another object of the invention to provide an actuator, wherein the pneumatic function operates substantially independently of the system water pressure.
It is yet another object of the invention to provide an actuator which will not trigger the system in the event of an electrical power failure.
It is again another object of the invention to provide an actuator which will not reset itself during a fire due to an air pressure surge.
These and other objects of the invention will be apparent upon consideration of the following drawings and detailed description of the preferred embodiments.